1. Technical Field
The present disclosure relates to an insulated gate semiconductor device which supplies power to a load by switching an insulated gate semiconductor element, such as an IGBT or a power MOS-FET.
2. Description of Related Art
As a drive device which drives a load such as a motor, a semiconductor device which, by switching and driving a semiconductor element such as a transistor, converts input power to power suitable for driving the load, is known. FIG. 4 is a main portion outline configuration diagram showing one example of this kind of semiconductor device 1 which is introduced in detail in, for example, JP-A-2010-88036.
The semiconductor device 1 includes a diode bridge circuit DB, which rectifies input alternating current power AC, and a converter 2 which converts the output of the diode bridge circuit DB to direct current power of a predetermined voltage. The semiconductor device 1 further includes a chopper circuit 3 which boosts and supplies the direct current power, obtained from the converter 2, to a load RL such as a motor.
Incidentally, the converter 2 includes a switching element S1, formed of, for example, a MOS-FET, which switches the output of the diode bridge circuit DB, at a predetermined frequency, via the primary winding of an isolation transformer T. The converter 2 further includes a rectifying and smoothing circuit formed of a diode D1, which rectifies and outputs a voltage generated in the secondary winding of the isolation transformer T, and a capacitor C1 which smoothes the output of the diode D1. The converter 2 of a flyback type configured in this way, by controlling, for example, the on-width of the switching element S1 using a main control section 4, controls an output voltage generated in the secondary winding of the isolation transformer T.
Also, the chopper circuit 3 includes an inductor L, to which is applied the output voltage of the converter 2, and a switching element S2 which controls a current flowing through the inductor L. The switching element S2 on-operates when a predetermined gate voltage is applied from a drive section 5, and accumulates power energy in the inductor L. The power energy accumulated in the inductor L is emitted from the inductor L by an off-operation of the switching element S2. Further, the power energy emitted from the inductor L, after being accumulated in a capacitor C2 via a diode D2, is supplied to the load RL as a direct current voltage. Incidentally, the switching element S2 is formed of, for example, a junction FET, superior in high speed followability, which is used in a unipolar mode.
Herein, the semiconductor device 1 includes a current detection section 6 which detects an output current supplied to the load RL from the chopper circuit 3 or a current flowing through the switching element S2. The current detection section 6 assumes the role of detecting whether or not the current supplied to the load RL exceeds a preset threshold value, that is, an overcurrent. Also, the voltage control section 7, when an overcurrent is detected by the current detection section 6, drives the switching element S2 in a bipolar mode by setting a gate voltage output by the drive section 5 to be higher than a built-in voltage of the switching element S2. In this way, the on-resistance of the switching element S2 is kept low by causing the switching element S2 to operate in the bipolar mode when an overcurrent is detected. Further, an overheat destruction of the switching element S2 due to an overcurrent is prevented.
In FIG. 4, temperature monitoring section 8 detects an operating temperature of the switching element S2 from the current flowing through the gate of the switching element S2, which is detected via a resistor R. The respective on-widths of the switching elements S1 and S2 are feedback controlled in response to the operating temperature of the switching element S2 detected by the temperature monitoring section 8, and the output voltage for the load RL is stabilized.